ISTANBUL— Turkish police have detained at least 49 people in Istanbul and Ankara as part of a high-level corruption probe into alleged bribery connected to public tenders. The move is being widely interpreted as a challenge to the authority of Prime Minister Recep Tayyip Erdoğan.

Istanbul’s police chief Huseyin Capkin was dismissed Thursday, in the latest fallout from one of Turkey's largest-ever judicial probes into government corruption. The sons of senior ministers, including the Interior Minister, were detained, as were numerous high-level bureaucrats, and dozens of senior police officers have been fired or reassigned. The government claims the officers failed to inform their superiors about the probes. Observers say the investigation is expected to grow, and they predict that prosecutors will call for the parliamentary immunity of the implicated ministers to be rescinded.

Cengiz Aktar of the Istanbul Policy Group think tank says the investigation is one most serious in the country’s history.

"It's revolutionary; nothing of the kind happened in this country before. Of course, corruptions always existed like everywhere in the world. But the scale and the persons involved, indicted - it's unique," said Aktar.

The investigation centers on the alleged laundering of money from Iran to circumvent international sanctions on Tehran, and alleged bribery in the awarding of state contracts for land development. The Turkish media have broadcast pictures of millions of dollars in cash, found at the home of one of the three sons of government ministers detained, as well as the home of a senior official of the state-owned Halkbank.

But Prime Minister Recep Tayyip Erdoğan is taking a robust stand against the investigation, claiming it is part of a conspiracy against his government.

"There is a very dirty operation here,” Erdoğan said Thursday. "Some circles inside and outside of Turkey are seeking to hinder Turkey from its rapid growth."

Observers say the prime minister sees a powerful Islamist movement led by the cleric Fethullah Gulen as being behind the probe. Gulen's followers are widely believed to be influential both in the judiciary and the police.

But Gulen, who lives in self-imposed exile in the United States, denies the accusation. He was once a strong backer of the Islamist-rooted ruling AK Party, particularly in its struggle against the once-dominant army. But tensions have been on the rise in the last 18 months.

Asli Aydintasbas, a political columnist for Turkey’s Milliyet newspaper, says Erdogan will try and use the struggle with Gulen’s supporters to his advantage.

"There is no doubt that part of this is the power struggle between the Gulenists and the government. The government’s line will be foreign plot and the Gulenists are working for foreign interests - Israel, US. It's in their interest; Erdogan has always benefited from looking like victim, David and Golia[th]," said Aydintasbas.

Observers say the government will be keen to make the judicial investigations be about democracy rather than corruption. But analyst Aktar says if the allegations stick, the consequences for the AK Party could be severe.

"The constituency of the ruling party is composed mainly of destitute masses, and the sums involved mentioned in the press, millions and billions, that might have indeed a quite negative effect on the AK, which is preparing for the next round of elections 2014 and 2015," said Aktar.

Turkey is heading into an 18-month election cycle, with crucial local elections in March, followed by presidential elections in which Erdoğan is widely expected to run and a general election in 2015. The anti-corruption probe could not come at a worse time for the government, and many of its supporters insist this is not a coincidence. Observers say how successful the government is in convincing the country that the probe is more a conspiracy than a corruption investigation could determine the outcome of the upcoming elections.

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